As described in German patent document 3,140,353 filed 10 Oct. 1980 by F. Wagner, German patent 2,805,038 of H. Oberdorfer, and in German utility model 7,827,429 published 08 May 1980, a standard ceramic-plate flow-control valve has a housing having a chamber into which opens a port, a ceramic valve plate fixed in the chamber over the port, formed with a throughgoing aperture aligned with the port, and having a substantially planar face, and a ceramic control plate having a substantially planar face lying flatly on the valve-plate face and formed with a throughgoing aperture. The control plate can be pivoted relative to the valve plate about an axis substantially perpendicular to and traversing the surfaces between an open position and a closed position. In the open position the control-plate aperture overlaps the valve-plate aperture for flow through the two apertures. In the closed position the control-plate aperture is aligned axially with a portion of the valve-plate face and is offset angularly from the valve-plate aperture and the valve-plate aperture is aligned axially with a portion of the control-plate face and is offset angularly from the control-plate aperture.
Such a valve can be used as a finely adjustable flow-control valve and/or as a shutoff valve. The valve is typically moved from the fully open to the fully closed position by pivoting a handle through at most 180.degree., and normally has a very smooth action.
The main disadvantage of such a valve is that it leaks if the plate faces are damaged at all. Thus if grit from the liquid passing through the valve gets between these faces, each time the valve is actuated it abrades both faces and damages them, leading inevitably to leakage. This type of wear is a particular problem in the annular outer-edge region that is never overlain by the plate apertures, since any material trapped here is not flushed out during the normal operation of the valve. Furthermore the valve can dry out in the nonoverlap regions and become sticky.